Six months ago, Google publicly wiped out any co.cc domain from showing in Google's search results. That subdomain wide penalty seems to have now been lifted.
A search for [site:co.cc] returns over a 100 million results now:

The results started appearing about ten days ago, when before, it returned nothing:

I am not sure if Google changed their mind of this penalty was automatically lifted after a certain time period? Who knows if the subdomain will be banned again when Googlers return from their holiday break.
But at least now you can check to see just how spammy the co.cc sites are.
Forum discussion at Google Webmaster Help.

Comments:
Sunny Ujjawal
12/31/2011 12:13 pm
At last you have published this info provided by me. I was waiting for a long time for co.cc because i am having so many domains in it. Congrats co.cc Team and Thanks Google !
Barry Schwartz
12/31/2011 10:43 pm
Thank you
Jeff Downer Indianapolis IN
01/01/2012 03:43 pm
Does this mean much if the co.cc domains will be ranked at the bottom of the results? I suspect these domains will only rank well for the longest tailed of keywords.
Lars-Göran Frey
05/30/2012 08:43 pm
I hope my co.cc get back on google top 10 search http://www.smslan.co.cc
Vivek Sancheti
12/12/2012 06:53 pm
what happend to them now ? they are dead ? even main page www . co .cc is not opening !